1. Field of the Invention
This invention relates to the beneficiation of potash ores and, more particularly, relates to the removal of insoluble slimes from sylvinite ores through an improved froth flotation technique wherein specific collector reagents are utilized to both effect the flotation of the slimes and render residual insoluble slimes inert during subsequent flotation to recover sylvite (KCl).
2. Description of the Prior Art
The recovery of sylvite from sylvinite ores is known to be most efficiently achieved through the technique of froth flotation. However, such ores normally include impurities in the form of insoluble slimes, such as clays, other silicates and the like. Commercial desliming of sylvinite ores is usually accomplished by some form of mechanical separation technique, such as hydroclassification apparatus, including cyclone separators. Typically, the sylvinite ore pulp is passed through the cyclone and the overflow, after thickening, is discarded. However, this method usually results in the removal of a substantial portion of the sylvite values in the ore along with the slimes. Accordingly, the sylvite lost in the desliming is not available for recovery in the subsequent sylvite flotation of the ore, thereby reducing the sylvite recovered in this latter step.
Large tonnages of high-grade, low-water-insoluble-content sylvinite ores have been processed in the Permian Basin region in Carlsbad, New Mexico during the past forty years. These deposits are being rapidly depleted, thereby leaving large reserves of lower grade ore. This lower grade sylvinite ore contains 1% to 8% water-insoluble slimes, commonly referred to as insol slimes. These insol slimes must be removed prior to potash or sylvinite flotation because of their high adsorptive capacity for amines utilized in conventional potash flotation. The insol slimes are conventionally removed by scrubbing the ore particles, followed by hydroclassification, as earlier described, to separate the slimes from the coarse sylvinite ore. Any residual insol slimes not removed by the desliming procedure are blinded with suitable reagents, such as guar gum or starch, to prevent interference in subsequent potash flotation. Potash losses in the deslime product and process brine requirements increase as the insol content increases.
Presently known mechanical desliming methods are inadequate for processing sylvinite ores containing greater than 4% insol slimes because of high K.sub.2 O loss in the deslime product, excessive brine requirements, and depression of subsequent KCl flotation by residual insol slimes not removed in the deslime stage. Methods heretofore developed to remove insol slimes by froth flotation of the flocculated slimes have been unsatisfactory because the residual insol slimes not removed during flotation serve to depress the subsequent KCl flotation, even when excessive amounts of slime blinder are used.
Various collector reagents have been used for removal of insol slimes by selective froth flotation of such slimes from sylvinite ores, with all such processes requiring that the insol slimes be initially flocculated prior to the addition of the flotation collector reagent in order to reduce the effective surface area of the insol slimes and prevent high absorption of the reagent by the slimes.
Such reagent schemes include using an acrylamide polymer flocculant and a frother, such as cresylic acid or methylisobutyl carbinol (MIBC), to float insol slimes. Another such process utilizes a high molecular weight cationic polymer to selectively flocculate insol slimes, after which the flocculated slimes are floated using a long chain carboxylicamine reaction product. A further process is also known utilizing an oxidized mixture of white spirit and acidol, and oxyethylated synthetic fatty acids as flotation collectors for flocculated insol slimes. Still another technique involves the use of a polyacrylamide flocculant and a cationic surfactant that may be either a condensation product of ethylene oxide with various organic nitrogen containing compounds or a quaternary ammonium chloride compound having at least one long chain alkyl group containing 12 to 18 carbons or a long chain acyl (alkyl-CO) group.
However, none of the above described reagent schemes utilizing selective froth flotation for the removal of insol slimes from sylvinite ores deal with the effect of unremoved residual insol slimes on subsequent KCl flotation recovery.
It is therefore highly desirable that a method for removing insol slimes from sylvinite ores serves to reduce potash losses in the insol slimes product, lower the process brine requirements, and increase subsequent potash recovery after insol slimes removal.